In line to the throne: royal children worldwide

Britain

Catherine and William's baby will be third in line to succeed its great grandmother Queen Elizabeth II, the head of state of the United Kingdom and 15 other Commonwealth realms, including Australia and Canada.

The baby will follow its grandfather Prince Charles, the heir to the throne, and its father Prince William, the eldest child of Charles and the late Diana, princess of Wales.

Once all the realms have passed the legislation, male primacy will be brought to an end, backdated to October 2011.

Royal family: House of Windsor.

Belgium

Princess Elisabeth, aged 11, is the heir to the throne. Her father King Philippe - who is married to Princess Mathilde d'Udekem d'Acoz - became king after his father Albert II abdicated this month.

After Philippe's eldest daughter, who could become the first queen of the Belgians, their three other children follow: Gabriel, nine, seven-year-old Emmanuel, and Eleonore, five.

The law excluding women from becoming the monarch was repealed in 1991.

Royal family: House of Belgium.

Denmark

Prince Christian, seven, is second in line to the throne after his father, Crown Prince Frederik, the eldest son of Queen Margrethe II and Prince Consort Henrik.

He comes before his sister Isabella, six, the third in line to the throne.

The law which excluded women from the succession was repealed in 1953.

Royal family: House of Glücksburg.

Japan

Prince Hisahito, six, the only son of Prince Akishino (the younger brother of Crown Prince Naruhito), is third in line to the throne after his uncle and father, the children of Emperor Akihito.

Aiko, Princess Toshi, the 12-year-old only child of Naruhito and his wife Michiko, is not in line to inherit the throne, as females were excluded in 1889.

Royal family: Yamato Dynasty

Morocco

Prince Moulay Hassan, 10, the son of King Mohammed VI and Princess Lalla Salma, is the kingdom's crown prince. He has a sister, six-year-old Lalla Khadija, who is ruled out of the succession as a girl.

Royal family: Alawi Dynasty

The Netherlands

Princess Catharina-Amalia, nine, the oldest child of King Willem-Alexander and Queen Maxima, is first in line to the throne. She is followed by her sisters Alexia, eight, and Ariane, six. Under a 1983 law the eldest son or daughter becomes heir.

Royal family: House of Orange-Nassau.

Norway

Princess Ingrid Alexandra, nine, the first daughter of Crown Prince Haakon and Crown Princess Mette-Marit, is second in line to the throne.

She is followed by her seven-year-old brother Sverre Magnus. Since 1990, the eldest child assumes succession, whether a boy or a girl.

Royal family: House of Glücksburg.

Spain

Seven-year-old Leonor de Borbon, is second in line to succeed King Juan Carlos of Spain, after her father, Crown Prince Felipe.

The Spanish constitution currently allows a female heir to the throne only if she has no brothers. If she does not have a brother, Leonor could become the first female Spanish head of state since Isabelle II (1833-1868).

Her six-year-old sister Sofia is third in line to the throne.

Royal family: House of Bourbon.

Sweden

Princess Estelle, the daughter of Sweden's Crown Princess Victoria and Prince Daniel, who is 17 months old on Tuesday, is second in line to the throne, after her mother, the daughter of King Carl XVI Gustaf. In Sweden male primacy was abolished in 1980.